I read in the forum that giving the calling user those permissions will allow the script to be run successfully. I don't have that luxury unfortunately. Is there another way to execute an upgrade using this tool?

The user has database owner privileges, but they don't have any other server-wide privileges. They can run the package fine from the GUI but not from the command line...same issue as nnodari. If there was a /makedatabase:false switch or the switch nnodari suggested perhaps that would solve the problem.